There are many types of electrical systems that benefit from electrical isolation. Galvanic isolation is a principle of isolating functional sections of electrical systems to prevent current flow, meaning that no direct electrical conduction path is permitted between different functional sections. As one example, certain types of electronic equipment require that high-voltage components (e.g., 1 kV or greater) interface with low-voltage components (e.g., 10V or lower). Examples of such equipment include medical devices and industrial machines that utilize high-voltage in some parts of the system, but have low-voltage control electronics elsewhere within the system. The interface of the high-voltage and low-voltage sides of the system relies upon the transfer of data via some mechanism other than electrical current.
Other types of electrical systems such as signal and power transmission lines can be subjected to voltage surges by lightning, electrostatic discharge, radio frequency transmissions, switching pulses (spikes), and perturbations in power supply. These types of systems can also benefit from electrical isolation.
Electrical isolation can be achieved with a number of different types of devices. Some examples of isolation products include galvanic isolators, opto-couplers, inductive, and capacitive isolators. Previous generations of electronic isolators used two chips in a horizontal configuration with wire bonds between the chips. These wire bonds provide a coupling point for large excursions in the difference between the grounds of the systems being isolated. These excursions can be on the order of 25,000 V/usec.
As mentioned above, electrical isolation can be achieved with capacitive, inductive isolators, and/or RF isolators to transmit data across an isolation boundary. There have been some difficulties with developing and deploying capacitive isolators. For example, one issue that exists for capacitive isolators is that the dielectric material between the capacitive plates can be prone to electrical shorts/current leaks if the dielectric material is not of sufficient thickness. While this problem can be addressed by increasing the overall thickness of the dielectric material, increased dielectric thickness unfortunately results in reduced signal strength between the capacitive plates.
Another issue encountered by prior art capacitive isolators is that during fabrication of the top metal pattern, there could be metal remnants left behind after the etching process. These metal remnants can result in the creation of leakage paths between electrodes that are otherwise intended to be electrically isolated from one another. Thus current leakage could result in functional failure of the capacitive isolator.
Still another issue encountered by prior art capacitive isolators is that encapsulation stresses created due to conformal passivation may cause stress concentrations at the corners of metal edges on the substrate of the isolator. These stress concentrations can cause physical failure (e.g., decoupling) of the metal-to-substrate connection.